1. Field of the Invention
The invention relates to the field of imprint lithography and, in particular, to labeling an imprint lithography template prior to use within an imprint lithography machine.
2. Statement of the Problem
Imprint lithography involves applying a photo-curable liquid resist, or “photoresist”, onto a substrate with a mold, commonly referred to as an imprint lithography template. The template is generally made of a transparent material like quartz. After the template and the substrate are pressed together, the photoresist is cured by propagating UV light and/or heat through the template. The photoresist material that is exposed to the light becomes solid to pattern the substrate on a very small scale (e.g., 10 nm or less). After template separation, the pattern consists of the features in relief from a residual layer of photoresist, which may then be removed by an etch process to leave only the pattern features in the substrate.
The overall process of imprint lithography involves several steps, including surface preparation, photoresist coating, mask alignment, exposure, and excess photoresist removal. Because of the delicacy of the process, care is taken when preparing a surface for lithography. Surface contaminants are cleaned to ensure proper imprinting on the substrate. To remove the contaminants, the surface is soaked and rinsed. The surface is then primed with more chemicals to aid in the photoresist adhesion. After the surface is cleaned and primed, the photoresist is applied. Optimization is needed to apply the photoresist uniformly. The photoresist bonds uniformly to the surface. An optional pre-bake process includes heating the substrate in a convection oven or through a heated plate placed below the surface. The purpose of the pre-bake is to evaporate the excess coating solvent and to compact and harden the photoresist; however, not all imprint resists require a pre-bake. The lithography template is then aligned with the substrate. The molecules in the photoresist that are subjected to the UV light and/or heat are bonded strongly together in long chains via polymerization. The post bake process may be used to stabilize and harden the photoresist and remove traces of development chemicals from the substrate. Etching may then be used to remove the excess photoresist including a thin layer of resist between imprinted features.
Delicate alignment of the mask with respect to the substrate is necessary to ensure that the pattern is properly transferred. Moreover, the lithography template also requires delicate handling so as to not scratch the template because scratches transfer into the substrate as a defect. Generally, the template is prepared for the lithography process by placing the template in a lithography machine. If the template is placed in the lithography machine incorrectly (e.g., wrong side up), the template may scratch, thereby destroying the usefulness of the template. However, knowing which side of the template is to face the substrate is difficult as the template is transparent with no visible markings. One way to ensure that the template is properly placed in the lithography machine is to single handedly follow the template from the point of manufacture to its ultimate placement in the lithography machine. Such is generally not practical as there are many people, templates, lithography machines, etc. involved in the lithography process. Another manner to ensure that the template is properly processed and placed in the lithography machine includes marking the template in a boundary area that does not interfere with the UV light lithography such that the handler knows which side is up. For example, if the wrong side is up when being placed in the lithography machine, the handler knows because the marking appear backwards through the transparent template. However, present methods of marking are not permanent and the marks are removed due to the harsh chemicals that are used to clean the template after the lithography process. Thus, when the template is used again in a lithography machine, proper placement becomes an issue. Alternatively, the template may be etched with a laser or other etching means. Etching the template adds complication and may be acceptable as long as no particles or protrusions are created in the template surface. Accordingly, there exists a need to provide a relatively permanent label to the template that assists in preventing damage to the template during handling and does not create particles or protrusions on the imprint surface of the transparent template.